1. Field of the Invention
The invention relates to a power chain saw with a drive motor arranged in a housing, which drives a saw chain circulating on a saw guide, wherein the saw guide is held clamped by one end transversely to its surface plane between the housing and a tightening element.
2. Description of the Related Art
A power chain saw of the species is known from DE 38 43 459 A1, for example. A power chain saw is described in this document, wherein a drive motor arranged in a housing drives, by means of a chain wheel, a saw chain circulating on a saw guide. On its one end the saw guide is held clamped on the housing transversely to its surface plane between the housing and a tightening element. When the tightening element is detached, for tightening the saw chain the saw guide can be adjusted in the longitudinal direction by means of a chain tightening device. The chain tightening device is adjusted by means of an actuating screw, wherein a bolt engages the saw guide and is displaced along a slit in the crank housing. Following the completed adjustment of the chain tension, the tightening device is tightened, and the saw guide is clamped between the housing and the tightening element in the process. The facing surfaces between the end of the saw guide and the housing, or respectively the tightening element have been treated to increase their coefficients of friction, so that greater forces can act on the clamping without causing a displacement of the saw guide.
The disadvantage of this known technology is that, in spite of the treatment of the facing surfaces for increasing the coefficient of friction, a displacement of the saw guide in its longitudinal direction toward the housing is possible during operation. In connection with hard work in particular, when the chain is under a great load and the friction clutch between the motor and the chain, which is customarily provided, is partially released, practically all of the force which can be maximally attained prior to the release of the friction clutch acts in the longitudinal direction on the saw guide. Therefore frequent re-tightening of the chain is required. Another disadvantage is the tightening process itself. A relatively elaborate mechanism is required for clamping the saw guide with the required force in the longitudinal direction. In connection with devices for leisure time use in particular, it is necessary to principally avoid elaborate and therefore expensive solutions. But the force which can be manually exerted without assistance is insufficient for sufficiently tightening a saw chain. An opening provided in the saw guide, through which a lever is pushed, which can be supported on the housing, is also no sufficient, since such a tightening device could not be operated by one person alone, since it is necessary to simultaneously perform clamping and the tightening of the tightening device.
It is the object of the invention to present a power saw with a tightening device for the saw chain, which makes the simple adjustment of the chain tension by a single person possible, which moreover can be advantageously produced and which makes the regular re-tightening of the chain during operation unnecessary, even under greater stress.
The object is attained by a power chain saw having the characteristics of claim 1.
The power chain saw of the invention includes a housing, in which the drive motor is arranged. The drive motor drives a saw chain circulating on the saw guide. On its end facing the motor, the saw guide is held clamped transversely to its surface plane between the housing and a tightening element. With the tightening element detached, the saw guide can be displaced in the longitudinal direction for tightening the saw chain. The saw guide rests with one side against the housing and with the other side against the tightening element. Blocking means are arranged between the saw guide and the housing and/or the saw guide and the tightening element, which permit the displacement of the saw guide only in the longitudinal direction away from the housing, i.e. for tightening the chain, when the tightening element is detached. No displacement toward the housing is possible. The blocking means block the displacement in this direction.
Detent plates are preferably used as blocking means, which for example can be arranged between the saw guide and the tightening element. One detent plate is fixedly connected with the saw guide and is in contact with a correspondingly embodied detent plate fastened on the tightening element. The teeth of the detent plate are arranged in a sawtooth pattern in such a way that a displacement is only possible in the tightening direction of the chain. A displacement in the other direction is only possible after the almost complete detachment of the tightening element, so that the teeth of the correspondingly designed detent plates can no longer come into contact with each other.
The tightening element is preferably designed as a chain wheel protector.
In a preferred further development of the invention, an elastic element is arranged between the housing and the saw rail and/or the tightening element and the saw rail which, when the tightening element is detached, maintains the saw guide and the blocking element against each other with elastic prestress. The chain guide plate, for example, can function as such an elastic element. If the tightening element is slightly loosened, the elastic force of the elastic element acts in such a way that the saw guide is pushed against the oppositely located part of the power saw, i.e. either against the housing or against the tightening element. The blocking means, which are maintained in contact by the elastic force, are on the side located opposite the elastic element.
The invention will be explained in greater detail in what follows by means of the attached drawings.